King William Street was the northbound terminus of
the City & South London railway -
the world's first electric underground railway. Originally designed
to be cable hauled, the
line proved popular and the original terminii (Stockwell at its
southern end) were too small
to cope with the resultant passenger numbers.

The southbound tunnel north of the river.

Approaching King William St station site in the southbound tunnel. The brickwork
houses the toilets built for air-raid shelter use during World
War II.

A closer view of the cubicles.

Looking back in a southerly direction at the cubicles - the WWII shelter sign saying MEN is still partially intact.
(In fact the direction viewed is westerly, as the King William Street station site lies on an east/west axis. The tunnels head north from London Bridge, swing westward under the river, head north-easterly underneath Arthur Street and reach the terminus pointing eastward).

Approaching the station, the single tunnels branch out into a large dual tunnel, as seen in the photo below.

This photo, taken in the 1930s, shows the two tunnels joining up as they approach King William Street station. The southbound tunnel is the left hand one.

Reverse running operated on part of the line; between the road junction of Newington Causeway and Borough Road (between Elephant & Castle and Borough stations) and Swan Lane (just north of the river Thames). Thus the short distance between Swan Lane and King William Street station had 'normal' left hand running. No satisfactory explanation has been given for the reverse running.

When the line was extended northwards in 1900, the right hand running continued north of Elephant & Castle until there was sufficient clearance to build a new 'righting' of the tunnels (between Bank and Moorgate stations).

The southbound tunnel has a much steeper gradient: 1 in 14, as opposed to 1 in 40 for the northbound tunnel. The reason for this is that the southbound tunnel had to dive under the northbound one to allow the tunnels to be literally on top of each other as they passed under Swan Lane.
Due to fear of damage to buildings from tunnels underneath, it was common practice at this time to build tube tunnels underneath roads. Where the roads were narrow, the tunnels were built on top of each other, rather than side by side. This arrangement is still evident in some stations e.g. Kentish Town, South Kensington.

More recent photo showing the same area but with WWII air-raid shelter additions.

Parts of the tunnel mouths can be seen through the doorway in the centre of the photo, where the differing heights can be made out. The left hand tunnel has steps down to it, presumably installed when the station was converted to a World War II air raid shelter.

Closer view of the right hand (northbound) tunnel. There are cubicles built here as well, though only on one side of the tunnel. As the cubicles in the other tunnel were labelled MEN, the assumption is that these ones were used by women.

Old gradient painted indicator, still visible despite the rust.

The northbound tunnel and its cubicles. The view is facing away from King William Street station.

Heading further down the northbound tunnel away from King William Street station. This flood prevention door is built somewhere between the river's edge and Upper Thames Street. There is a large amount of condensation in the tunnel in this area and it is supposed that the water on the floor is largely through condensation as opposed to ingress.